1. Field of the Invention
The present invention relates to a computer system for monitoring data migration between storage areas in a storage device.
2. Description of the Related Art
In a computer system including computers and a storage device (hereinafter referred to as storage), generally, a computer (hereinafter referred to as “host computer” in order to distinguish the host computer from a management computer) uses storage areas provided by the storage for storing data. On this occasion, it is necessary to expand the capacity of a storage area (hereinafter referred to as “volume”) of the storage in accordance with increase in data stored by the host computer.
As an example of expansion of a volume in the storage, it was necessary to expand the volume after the operation of the computer system was once stopped so that the computer system was allowed to use the expanded volume again. Accordingly, the aforementioned volume expansion method had a disadvantage in that transactions executed by the computer system were suspended.
As measures against such transaction suspension, there has been proposed a technique for automatically expanding an insufficient capacity of a volume in a real storage in accordance with data to be written from a host computer into the volume while capacities of volumes of the storage to be recognized by the host computer are unchanged (see US2003/0009619 A1).
In the following description, a volume which can be managed in a storage due to increase in allocation from a physical area in the storage without any change in the capacities of volumes of the storage to be recognized by the host computer is referred to as “virtual volume”. In addition, a storage area of the storage for managing allocation to a virtual volume of a real physical area for expanding an insufficient capacity of the volume in accordance with data to be written from the host computer into the volume is referred to as “virtual pool” (or “virtual volume pool”). A volume to be registered in the virtual pool is referred to as “virtual pool volume”.
There is necessity for performing optimal allocation in accordance with the utility value of data because of safekeeping of the data for a long term due to legal restrictions, etc. For this reason, there is a technique of data migration in accordance with the utility value of data. As an example of this technique, there has been proposed a technique for managing a plurality of volumes collectively as a group and migrating data between the volumes in a hierarchical structure with a certain characteristic (see JP-A-2006-99748).
In the techniques described in the US2003/0009619 A1 and US2006/0047909 A1, there are problem as follows.
First, data migration between volumes obtained by automatically expanding capacities of the volumes in a storage, i.e. among virtual volumes must be performed in the same manner as data migration between conventional volumes. For this reason, data migration performed between the conventional volumes must be now performed between the virtual volumes.
That is, when data migration is executed, data stored in a virtual volume as a source of the data migration (hereinafter referred to as “source virtual volume”) is reflected on data in a virtual volume as a destination of the data migration (hereinafter referred to as “destination virtual volume”). When data migration is executed, there is however a problem that the data migration cannot be performed because the capacity of a physical area really allocated to the source virtual volume cannot be covered by the destination virtual volume.
In terms of data migration, the time to set a destination virtual volume and the time to really start the data migration may be different because of operation in the storage. In this case, data writing on a source virtual volume is performed even after the setting of data migration or after the start of data migration. For this reason, the capacity of the physical area really allocated to the source virtual volume changes before the data migration is completed.